The field of the invention relates generally to systems and, more particularly, to a signal testing apparatus that may be used with systems to verify signals, such as radio frequency (RF) signals.
At least some known systems, such as global navigation satellite systems (GNSSs), include a plurality of global navigation satellite vehicles (SVs) that provide autonomous geo-spatial positioning with global coverage. Such systems enable receivers, such as GNSS receivers, to determine their location (i.e., longitude, latitude, and altitude) to within a pre-defined distance using time signals, such as time RF signals, that are transmitted by radio transmitters from the SVs.
However, there are limitations as to how the receivers can test or verify the RF signals that are being transmitted by the SVs. For example, the receivers need to simultaneously track and measure the RF signals transmitted by at least 4 orbiting GNSS SVs in order to compute the receiver's position, velocity, and time (PVT) solutions. More specifically, the receivers are unable to form a PVT solution while the SV is on the ground. As a result, pre-launch verification of a SV involving actual receivers is limited to static tracking-only tests. These tests are considered inadequate in revealing issues that manifest when PVT solutions can be formed in a dynamic environment. Therefore, it can be difficult to verify the interoperability between receivers and a full constellation of SVs in space while the SVs are in the development stage. Moreover, it can be substantially cost prohibitive and difficult to fix implementation issues post-launch.